The present invention relates to valves and more particularly to poppet valves of the type operated by an electromagnetic force motor for purposes of effecting a zero leak seal when in closed condition.
Valves of the type described are employed for instance in aerospace applications to control the flow of fuel and/or oxidizer. Initially, attempts were made to create a zero leak seal by carefully machining mating sealing surfaces and providing for precise mounting of a poppet and valve seat during assembly thereof, but seals of this type are extremely difficult to fabricate. One example of this type of valve appears to be U.S. Pat. No. 3,373,769.
It has also been proposed to avoid the necessity of providing for accurate mounting of a poppet and valve seat during initial assembly of a valve by loosely mounting a poppet within a recess defined by a flapper, so as to permit the poppet to rotatably/tiltably position itself with respect to both the flapper and the valve seat each time the valve is closed, as required to provide a desired fluid seal. A drawback of this construction is that movements of the poppet relative to the flapper tend to occur whenever the valve is open and exposed to vibration and acceleration conditions. As a result, when the valve is subsequently closed, frictional effects between the poppet and the flapper and/or valve seat produces a hysteresis characteristic for the valve, which is not acceptable for many aerospace applications. A second drawback of this type of valve is that any movement of the poppet relative to the flapper while the valve is in open condition, also changes the orientation of the poppet relative to the valve seat and results in variations in flow through the valve. As a result, this type of valve is only adapted to provide for either full closed or full open flow conditions and cannot be employed to effect accurately controlled incremental variations or adjustments in fluid flow rate. One example of a valve appearing to have these characteristics is that disclosed in U.S. Pat. No. 3,510,100.
Although not directed to the type of valve herein contemplated, it has also been proposed to employ a low melting point adhesive, such as solder, to adhere a cap to a valve member or disc, as an incident to assembly of a valve in order to provide for proper positioning of the cap relative to a valve seat, as evidenced by U.S. Pat. No. 2,788,570.